The invention is in the field of electrochemical pumping of fluids, including electrochemical pumps and methods for inducing pressurization and/or flow of fluids.
Pressurization and manipulation of fluids on the nano- and micro-scale are required for a wide range of microfluidics applications, including analytical and synthetic “lab-on-a-chip”, ultra-small particle handling, and micro/nano-spray systems. Identical demands are key for smart structures and morphing technologies that incorporate plant-like nastic structures and/or individually addressable cells (Chopra, I., Amer. Inst. Aeronautics Astronautics J. 2002, 40, 2145; Loewy, R. G., Smart. Mater. Struct. 1997, 6, R11). A variety of micropumps have been developed for these applications. One classification system identifies micropumps as either displacement pumps or dynamic pumps (Laser, D. J. and Santiago, J. G., 2004, J. Micromech. Microeng., 14, R35-R64). Displacement pumps exert pressure forces on the working fluid through one or more moving boundaries. Dynamic pumps continuously add energy to the working fluid in a manner that increases either its momentum or its pressure directly and include ultrasonic, magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic or electrochemical actuation mechanisms.
Electrokinetic pumps produce fluid flow through electro-osmosis. In these pumps, a dielectric surface is placed in contact with an electrolyte and an electrically charged diffuse layer extends from the solid-liquid interface into the bulk of the electrolyte. The application of an electric potential to an electrolyte in contact with the dielectric surface produces a net force on the diffuse layer. U.S. Pat. No. 6,572,749, to Paul et al., describes an electrokinetic pump comprising at least one tube or channel forming a fluid passageway containing an electrolyte and having a porous dielectric medium disposed therein between one or more spaced electrodes. An electric potential is applied between the electrodes to cause the electrolyte to move in the microchannel by electro-osmotic flow. Silica particles having a diameter of about 100 nm to 6 microns are described as suitable for use as the porous dielectric medium. An ultra micro-porous material such as Vycor® porous glass or a Nafion® membrane was interposed between the electrode and the high-pressure fluid junction. These ultra micro-porous materials are described as capable of carrying current but having pores sufficiently fine that pressure-driven or electro-osmotic flow is negligible. It may be noted that there is some debate in the literature concerning the nano-scale structure of Nafion® material, although it is generally considered to have an effective or equivalent pore diameter of about 4 nm that is conditioning and counter-ion dependent (Mauritz, K. A. and Moore, R. B., 2004, Chem. Rev., 104, 4535-4585; Evans, C. E., Noble, R. D., Nazeri-Thompson, S., Nazeri, B., Koval, C. A., 2006, J. Membrane Sci., 279, 521-528).
The scientific literature describes micro-injectors and micro-dosing systems based on electrolytic gas generation. Lee et al. describe a micro injector actuated by bubbles generating by the boiling or electrolysis of an electrolyte in an actuator chamber (Lee, S. W. et al., 1998, Proc. 11th Annual Int. Workshop on Micro Electro Mechanical Systems, Heidelberg, Piscataway, N.J., IEEE). Böhm et al. describe a micromachined dosing system in which the driving force to dispense liquids originates from the electrochemical generation of gas bubbles by the electrolysis of water (Böhm, S. et al., 2000, J. Micromech. Microeng., 10, 498-504).
U.S. Pat. No. 4,118,299, to Maget, describes an electrochemical water desalination process relying on transport of protons and water through a cation exchange membrane. A salt-containing water stream is mixed with hydrogen and then pumped into an electrochemical cell whose anode and cathode are separated by a cation exchange membrane. The electrochemical cell ionizes hydrogen into protons which migrate to the counter electrode under the influence of an applied potential. The migrating protons entrain liquid water. At the counter-electrode, the migrating protons recombine to form hydrogen while releasing liquid water.
Redox batteries and fuel cells typically involve electrochemical cell compartments, each compartment containing one or more redox couples. The compartments are separated in some cases by an ion selective membrane. Several forms of redox fuel cells or batteries have been developed. U.S. Pat. No. 3,996,064 to Thaller describes a two-compartment cell. During passage of current through the cell, an anode fluid is directed through the first compartment at the same time that a cathode fluid is directed through the second compartment. Chloride salts in aqueous solution are described as useful anode and cathode fluids. U.S. Pat. No. 4,786,567 to Skyllas-Kazacos et al. describes vanadium redox batteries which employ V(V)/(IV) and V(III)/V(II) redox couples.
Finally, the art also includes pumps having a flexible diaphragm that can be used as reciprocating displacement micropumps. Reciprocating displacement micropumps are those in which moving surfaces do pressure work in a periodic manner. Several such pumps are described by Laser and Santiago (Laser, J. and Santiago, J. G., 2004, J. Micromech. Microeng., 14, R35-R64) Typically, a reciprocating displacement micropump comprises a pump chamber bounded on one side by the pump diaphragm, an actuator mechanism or driver, and two passive check valves, one check valve at the inlet (or suction side) and one at the outlet (or discharge side). As the pump diaphragm is oscillated, fluid is discharged on the “out stroke” and fluid is pulled into the pump on the “in stroke.” Typical oscillation frequencies range from 1 to 5000 Hz.
There remains a need in the art for additional devices and methods for producing fluid flow and/or pressurization using electrochemical means.